(1). Field of the Invention
The present invention relates to a process and a system for transferring vector signals through a signal transmission system or a data recording system. The signal transmission system may be a transmission line, a data writing and reading system in a digital recording device, and the like. Typically, the present invention can be applied to modem communication systems in the voice frequency band, high-speed modem communication systems for use in private branch networks, transmission systems for CATV, wireless transmission communication systems, optical fiber transmission apparatuses, and the like. In addition, the present invention also covers the technique of transmitting, and writing in and reading from a recording medium, a vector baseband signal.
(2). Description of the Related Art
For example, in the field of the modem transmission, i.e., transmissions of digital data through analog transmission lines, realization of a higher bit rate is required. For that purpose, ITU-T recommendation, V.34 provides a 28.8 kbps modem which uses a frequency band wider than the conventional modem transmission technique, within a Nyquist transmission technique.
In addition, in the field of the digital data recording devices such as magnetic disc devices, optical disc devices, digital video tape recorders, and the like, it is required to record digital data in these devices with a greater density so that the capacities of these devices are increased.
When realizing a 28.8 kbps modem by use of a Nyquist transmission method as used in the above technique of ITU-T recommendation, V.34, a frequency bandwidth of 3,200 Baud or 3,429 Bauds is required. That is, a wide frequency band is necessary to realize a high-speed modem by using a conventional data transmission method.
The frequency band width of the analog transmission line currently guaranteed in Japan is 0.3 Hz to 3.4 kHz, having a frequency bandwidth of 3,100 Hz. However, the frequency bandwidth of the above data transmission method, by use of the Nyquist transmission method, exceeds the above guaranteed frequency bandwidth of the analog transmission line. Therefore, the data transmission rate of 28.8 kbps cannot be guaranteed.
In addition, inter-code interference, white noise, timing jitter and the like sensitively depend on the frequency bandwidth of the transmission line. Therefore, it is desirable to maintain the frequency bandwidth within a conventionally guaranteed range of the analog transmission line.
In order to improve a coding gain, it is recently reported that the partial-response maximum-likelihood technique is applied to data writing and reading systems in the digital data recording devices. Nikkei Electronics, No. 599 (Jan. 17, 1994, in Japanese), pages 71 to 79, summarizes such applications of the partial-response maximum-likelihood process to the digital data recording devices.
However, in the partial-response maximum-likelihood method conventionally used in digital recording devices, signal points are configured on a one-dimensional line. Therefore, a large record area is required on record media, and there is a limit in increasing record density.